This invention relates to an apparatus for use with an automotive vehicle supported on a road surface by a pair of driven road wheels and a pair of non-driven road wheels to control an output transmitted from an internal combustion engine to the driven road wheels through an automatic transmission adapted to produce changes up based on engine output and vehicle speed.
A throttle valve is situated for rotation with an intake passage to control the amount of air permitted to enter an internal combustion engine through the intake passage, and thus the engine output torque transmitted from the engine to the driven road wheels of an automotive vehicle through an automatic transmission adapted to produce changes up based on engine output and vehicle speeds. In order to avoid lateral vehicle motions resulting from a great degree of slip of the road wheels during vehicle acceleration on an iced or snow-covered road surface, it has been proposed to perform a traction control with the use of an auxiliary throttle valve placed for rotation within the intake passage at a position upstream of the throttle valve. For the traction control, the auxiliary throttle valve is rotated in a closing direction to reduce the engine output torque and thus the driving forces transmitted to the driven road wheels when the difference between the speeds of rotation of the driven and non-driven road wheels.
It is preferable to further reduce the tendency of the road wheels to slip by advancing the time at which a change up is produced in the automatic transmission so as to reduce the driving torque transmitted to the driven road wheels during the traction control. However, this engine output control causes the engine speed from overshooting and undershooting a required value repetitively until the slip is converged below a predetermined degree. The degree of slip of the driven road wheels will increase particularly when the engine speed overshoots the required value.